= Spring for Apache Kafka Contributor Guidelines

Do you have something you'd like to contribute to **Spring for Apache Kafka**?
We welcome pull requests, but ask that you carefully read this document first to understand how best to submit them;
what kind of changes are likely to be accepted; and what to expect from the Spring team when evaluating your submission.

Please refer back to this document as a checklist before issuing any pull request; this will save time for everyone!

== Code of Conduct
This project adheres to the Contributor Covenant link:CODE_OF_CONDUCT.adoc[code of conduct].
By participating, you  are expected to uphold this code. Please report unacceptable behavior to
spring-code-of-conduct@pivotal.io.

== Understand the basics

Not sure what a *pull request* is, or how to submit one?  Take a look at GitHub's excellent documentation:
https://help.github.com/articles/using-pull-requests/[Using Pull Requests] first.

== Search GitHub ticket first; create an issue if necessary

Is there already an issue that addresses your concern?  Search the
https://github.com/spring-projects/spring-kafka/issues[GitHub issue tracker] to see if you can find something similar.
If not, please create a new issue before submitting a pull request unless the change is truly trivial, e.g. typo fixes,
removing compiler warnings, etc.

== Sign the contributor license agreement

If you have not previously done so, please fill out and
submit the https://cla.pivotal.io/sign/spring[Contributor License Agreement (CLA)].

Very important, before we can accept any *Spring Kafka contributions*, we will need you to sign the CLA.
Signing the CLA does not grant anyone commit rights to the main repository, but it does mean that we can accept your contributions, and you will get an author credit if we do.

== Fork the Repository

1. Go to https://github.com/spring-projects/spring-kafka[https://github.com/spring-projects/spring-kafka]
2. Hit the "fork" button and choose your own GitHub account as the target
3. For more detail see https://help.github.com/fork-a-repo/[Fork A Repo].

== Setup your Local Development Environment

1. `git clone --recursive git@github.com:<your-github-username>/spring-kafka.git`
2. `cd spring-kafka`
3. `git remote show`
_you should see only 'origin' - which is the fork you created for your own GitHub account_
4. `git remote add upstream git@github.com:spring-projects/spring-kafka.git`
5. `git remote show`
_you should now see 'upstream' in addition to 'origin' where 'upstream' is the SpringIO repository from which releases are built_
6. `git fetch --all`
7. `git branch -a`
_you should see branches on origin as well as upstream, including 'main'_

== A Day in the Life of a Contributor

* _Always_ work on topic branches (Typically use the GitHub issue ID as the branch name).
  - For example, to create and switch to a new branch for issue GH-123: `git checkout -b GH-123`
* You might be working on several different topic branches at any given time, but when at a stopping point for one of those branches, commit (a local operation).
* Please follow the "Commit Guidelines" described in
https://git-scm.com/book/en/Distributed-Git-Contributing-to-a-Project[this chapter of Pro Git].
* Then to begin working on another issue (say GH-101): `git checkout GH-101`. The _-b_ flag is not needed if that
branch already exists in your local repository.
* When ready to resolve an issue or to collaborate with others, you can push your branch to origin (your fork),
e.g.: `git push origin GH-123`
* If you want to collaborate with another contributor, have them fork your repository (add it as a remote) and
`git fetch <your-username>` to grab your branch.
Alternatively, they can use `git fetch --all` to sync their local state with all of their remotes.
* If you grant that collaborator push access to your repository, they can even apply their changes to your branch.
* When ready for your contribution to be reviewed for potential inclusion in the main branch of the canonical
spring-kafka repository (what you know as 'upstream'), issue a pull request to the SpringSource repository
(for more detail, see https://help.github.com/articles/using-pull-requests/[Using pull requests]).
* The project lead may merge your changes into the upstream main branch as-is, he may keep the pull request open yet
add a comment about something that should be modified, or he might reject the pull request by closing it.
* A prerequisite for any pull request is that it will be cleanly merge-able with the upstream main's current state.
**This is the responsibility of any contributor.**
If your pull request cannot be applied cleanly, the project lead will most likely add a comment requesting that you make
it merge-able.
For a full explanation, see https://git-scm.com/book/en/Git-Branching-Rebasing[the Pro Git section on rebasing].
As stated there: _"> Often, you’ll do this to make sure your commits apply cleanly on a remote branch — perhaps in a
project to which you’re trying to contribute but that you don’t maintain."_

== Keeping your Local Code in Sync
* As mentioned above, you should always work on topic branches (since 'main' is a moving target). However, you do want
to always keep your own 'origin' main branch in synch with the 'upstream' main.
* Within your local working directory, you can sync up all remotes' branches with: `git fetch --all`
* While on your own local main branch: `git pull upstream main` (which is the equivalent of fetching upstream/main
and merging that into the branch you are in currently)
* Now that you're in synch, switch to the topic branch where you plan to work, e.g.: `git checkout -b GH-123`
* When you get to a stopping point: `git commit`
* If changes have occurred on the upstream/main while you were working you can synch again:
    - Switch back to main: `git checkout main`
    - Then: `git pull upstream main`
    - Switch back to the topic branch: `git checkout GH-123` (no -b needed since the branch already exists)
    - Rebase the topic branch to minimize the distance between it and your recently synched main branch: `git rebase main`
(Again, for more detail see https://git-scm.com/book/en/Git-Branching-Rebasing[the Pro Git section on rebasing]).
* **Note** You cannot rebase if you have already pushed your branch to your remote because you'd be rewriting history
(see **'The Perils of Rebasing'** in the article).
If you rebase by mistake, you can undo it as discussed
https://stackoverflow.com/questions/134882/undoing-a-git-rebase[in this StackOverflow discussion].
Once you have published your branch, you need to merge in the main rather than rebasing.
* Now, if you issue a pull request, it is much more likely to be merged without conflicts.
Most likely, any pull request that would produce conflicts will be deferred until the issuer of that pull request makes
these adjustments.
* Assuming your pull request is merged into the 'upstream' main, you will actually end up pulling that change into
your own main eventually, and at that time, you may decide to delete the topic branch from your local repository and
your fork (origin) if you pushed it there.
    - to delete the local branch: `git branch -d GH-123`
    - to delete the branch from your origin: `git push origin :GH-123`

== Maintain a linear commit history

When merging to main, the project __always__ uses fast-forward merges.
When issuing pull requests, please ensure that your commit history is linear.
From the command line you can check this using:

----
log --graph --pretty=oneline
----

As this may cause lots of typing, we recommend creating a global alias, e.g. `git logg` for this:

----
git config --global alias.logg 'log --graph --pretty=oneline'
----

This command, will provide the following output, which in this case shows a nice linear history:

----
* c129a02e6c752b49bacd4a445092a44f66c2a1e9 INT-2721 Increase Timers on JDBC Delayer Tests
* 14e556ce23d49229c420632cef608630b1d82e7d INT-2620 Fix Debug Log
* 6140aa7b2cfb6ae309c55a157e94b44e5d0bea4f INT-3037 Fix JDBC MS Discard After Completion
* 077f2b24ea871a3937c513e08241d1c6cb9c9179 Update Spring Social Twitter to 1.0.5
* 6d4f2b46d859c903881a561c35aa28df68f8faf3 INT-3053 Allow task-executor on <reply-listener/>
* 56f9581b85a8a40bbcf2461ffc0753212669a68d Update Spring Social Twitter version to 1.0.4
----

If you see intersecting lines, that usually means that you forgot to rebase you branch.
As mentioned earlier, **please rebase against main** before issuing a pull request.

== Mind the whitespace

Please carefully follow the whitespace and formatting conventions already present in the framework.

1. Tabs, not spaces
2. Unix (LF), not DOS (CRLF) line endings
3. Eliminate all trailing whitespace
4. Wrap Javadoc at 90 characters
5. Aim to wrap code at 120 characters, but favor readability over wrapping
6. Preserve existing formatting; i.e. do not reformat code for its own sake
7. Search the codebase using `git grep` and other tools to discover common
   naming conventions, etc.
8. Latin-1 (ISO-8859-1) encoding for Java sources; use `native2ascii` to convert
   if necessary

== Add Apache license header to all new classes

[source, java]
----
/*
 * Copyright 2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package ...;
----

== Update license header to modified files as necessary

Always check the date range in the Apache license header. For example, if you've modified a file in 2016 whose header
still reads

[source java]
----
 * Copyright 2002-2011 the original author or authors.
----

then be sure to update it to 2016 appropriately

[source java]
----
 * Copyright 2002-2016 the original author or authors.
----

== Use @since tags

Use @since tags for newly-added public API types and methods e.g.

[source java]
----
/**
 * ...
 *
 * @author First Last
 * @since 3.0
 * @see ...
 */
----

== Submit JUnit test cases for all behavior changes

Search the codebase to find related unit tests and add additional @Test methods within. It is also acceptable to submit test cases on a per GitHub issue basis.

== Squash commits

Use `git rebase --interactive`, `git add --patch` and other tools to "squash" multiple commits into atomic changes.
In addition to the man pages for git, there are many resources online to help you understand how these tools work.

== Use your real name in git commits

Please configure git to use your real first and last name for any commits you intend to submit as pull requests. For example, this is not acceptable:

    Author: Nickname <user@mail.com>

Rather, please include your first and last name, properly capitalized, as submitted against the SpringSource contributor license agreement:

    Author: First Last <user@mail.com>

This helps ensure traceability against the CLA, and also goes a long way to ensuring useful output from tools like `git shortlog` and others.

You can configure this globally via the account admin area GitHub (useful for fork-and-edit cases); globally with

    git config --global user.name "First Last"
    git config --global user.email user@mail.com

or locally for the *spring-kafka* repository only by omitting the '--global' flag:

    cd spring-kafka
    git config user.name "First Last"
    git config user.email user@mail.com

== Run all tests prior to submission

See the https://github.com/spring-projects/spring-kafka#checking-out-and-building[checking out and building]
section of the README for instructions.
Make sure that all tests pass prior to submitting your pull request.

== Mention your pull request on the associated GitHub issue

Add a comment to the associated GitHub issue(s) linking to your new pull request.

== Provide a Link to the GitHub issue in the Associated Pull Request

There are multiple ways to link a Pull Request to a GitHub issue as described
https://help.github.com/en/github/managing-your-work-on-github/linking-a-pull-request-to-an-issue[here].

One way would be to add a GitHub issue link to your first commit comment of the pull request on the second line,
so your commit message may look like this:

----
    GH-1: Add Contribution Guidelines

    Fixes GH-1 (https://github.com/spring-projects/spring-kafka/issues/1)

    * add `CONTRIBUTING.adoc` describing the Contribution procedure
    * mention Contribution Guidelines in the `README.md`
    * mention CODE_OF_CONDUCT in the `README.md`
----

Also by using specific
https://help.github.com/en/github/managing-your-work-on-github/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword[keywords]
you can link to a GitHub issue like so:

    Closes #10
